Rotor for an electric machine

Abstract

 The rotor (1) for an electric machine comprises a rotor body (3) with a longitudinal axis (2), conductors (6) on the rotor (1), a liner sheet (8) around the rotor body (3) and conductors (6). The liner sheet (8) has parts (10) with lateral borders (14) that are not parallel to the longitudinal axis (2).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a rotor for an electric machine. For example the electric machine can be a synchronous generator such as a turbogenerator (i.e. a generator to be connected to a gas and/or steam turbine) or a hydro generator (i.e. a generator to be connected to a hydro turbine). Anyhow in different examples the electric machine can also be a different rotating electric machine such as an asynchronous generator, a synchronous or asynchronous motor.

BACKGROUND

[0002] Rotors of electric machines include a rotor body, for example comprising a rotor active part and rotor shafts at the ends thereof. The rotor active part has slots housing insulated conductors. At the ends of the rotor active part, rotor end windings are provided (around the shafts) to connect the conductors housed in different slots together and define a rotor winding.

[0003] Around the rotor end windings a retaining ring insulation is provided; in addition, above the retaining ring insulation and connected to the terminal part of the rotor active part, retaining rings are provided, to withhold the rotor end windings against centrifugal forces. The connection of the retaining rings to the rotor active part is achieved by heating the retaining rings and slipping them above the rotor active part.

[0004] Since when they are slipped above to the rotor active part and connected to it, the retaining rings are hot, they could damage the insulation of the insulated conductors and/or retaining ring insulation; for this reason a liner sheet around each retaining ring insulation is provided. The retaining rings are then connected above the liner sheet.

[0005] The liner sheet includes two or more cylindrical sections with facing straight lateral borders parallel to the rotor axis.

[0006] In order to fix the position of the lateral borders, protruding fingers extend from each cylindrical section; these fingers are housed in ventilation slots of the rotor active part.

[0007] This structure could cause drawbacks.

[0008] In fact, during operation the fingers could deform, this could cause the lateral borders to move away from their prefixed positions.

[0009] In case the lateral borders move to a zone above the insulated conductors, the lateral borders rest along a straight line above the insulated conductor insulation and retaining ring insulation; it was ascertained that this could damage the insulated conductor insulation and/or retaining ring insulation.

[0010] In other circumstances, when the borders move to a zone above a pole separation wedge (i.e. those wedges provided between adjacent conductors at the rotor end winding), the pole separation wedge could damage the retaining ring insulation.

SUMMARY

[0011] An aspect of the disclosure includes providing a rotor addressing the above-mentioned drawbacks of the known rotors.

[0012] These and further aspects are attained by providing a rotor in accordance with the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Further characteristics and advantages will be more apparent from the description of a preferred but non-exclusive embodiment of the rotor, illustrated by way of non-limiting example in the accompanying drawings, in which:

Figure 1 is a schematic view of a part of a rotor;

Figures 2 through 7 are schematic views (in a plane) of a part of the liner sheet (figures 2, 4, 6) and of a liner sheet portion (figures 3, 5, 7);

Figure 8 is a further schematic view (in a plane) of a part of a liner sheet;

Figure 9 is a part of a rotor with a mounting stop applied on it;

Figures 10 and 11 are schematic views of the mounting stop;

Figure 12 is a schematic cross section through the rotor end winding;

Figure 13 is a schematic view of a rotor; and

Figure 14 is a perspective schematic view of a liner sheet.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0014] With reference to the attached figures, a rotor 1 with a longitudinal axis 2 (this is a symmetry axis and an axis around which the rotor rotates during operation) includes a rotor body 3 defining a rotor active part 4 and rotor shafts 5 at the ends thereof.

[0015] The rotor 1 has slots that house conductors 6. These conductors 6 have a conductive bar made for example of copper and insulation around it. The conductors 6 are connected together to define a rotor winding; in this respect the conductors have portions 7 projecting from the slots of the rotor body 3, bent around the shafts 5 and connected together (end windings).

[0016] In the embodiment shown in the figures, around the portions 7 there are wrapped retaining ring insulation 50, a liner sheet 8 around the retaining ring insulation 50, a damper ring 51 around the liner sheet 8 and damper finger sectors 52 around the damper ring 51 and partially housed in the slots.

[0017] Then, around the liner sheet 8, a retaining ring 9 is provided.

[0018] The liner sheet 8 is defined by two or more parts 10, for example having a cylindrical sector shape. Each part 10 has a front and rear border 12, 13 respectively facing the rotor and facing away from the rotor, and lateral borders 14. The lateral borders 14 of different parts 10 face each other.

[0019] The lateral borders 14 are not parallel to the rotor axis 2. Since the lateral borders 14 are not parallel to the rotor axis 2, even if during operation they rest above a portion 7 of a conductor, they do not damage the retaining ring insulation 50, because the edges of the conductors and of the liner sheets are not in line (i.e. aligned).

[0020] In addition, between the portions 7 pole separation wedges are provided. If the lateral borders 14 are at a zone of the pole separation wedges, they are able to support a large part of the pole separation wedges, such that the pole separation wedges do not damage the retaining ring insulation.

[0021] For example, the liner sheet borders are:

• at an angle to the longitudinal axis (figures 2 and 3),
• saw shaped (figures 4 and 5),
• wave shaped (figures 6 and 7).

[0022] Other examples are anyhow possible.

[0023] Thanks to this structure a precise positioning of the liner sheet 8 (and in particular of the borders 14 thereof) is not mandatory.

[0024] Anyhow, each part 10 can also have a seat 22 for a mounting stop 23 (figure 9).

[0025] The mounting stop 23 can be removably connected during mounting to the parts 10; in addition the mounting stop can also be removably connected to the rotor body 3. For example it can be inserted into ventilating slots of the rotor body 3. The removing stop can define the position of the liner sheet 8 (and thus of the borders 14 thereof) without the risks of troubling situation during operation, because it is applied during assembling but it is then removed for operation (i.e. during operation the removing stop 23) is not connected to the rotor 1.

[0026] Pole separation wedges 25 are provided between adjacent portions 7 of the conductors 6 (end windings); these wedges 25 are used to mechanically connect together adjacent portions 7 coming from adjacent slots.

[0027] During operation, because of centrifugal forces, a gap 26 between adjacent lateral borders 14 of adjacent parts 10 is defined or is made larger.

[0028] Advantageously, the gap 26 is asymmetric to a radial axis 27 passing through the center of gravity 28 of the pole separation wedge 25.

[0029] This lets the pole separation wedge be covered by the parts 10 of the liner sheet 8 for a large part thereof, such that damages and break risks are reduced.

[0030] In particular, as shown in figure 12, a spring 30 can be provided to circumferentially press the pole separation wedge 25 (as indicated by arrow F).

[0031] The gap 26 is at the spring 30, preferably above the spring 30.

[0032] Even if the gap 26 only forms (due to centrifugal forces) during operation, its width can be calculated.

[0033] In a different embodiment, the borders 14 can be located at the pole separation. This prevents the retaining ring insulation from damage caused for example by the pole separation wedges pressing to it, because more supporting area is provided.

[0034] The rotor with the liner sheet according to the disclosure is useful in particular during assembling.

[0035] In fact, during assembling the rotor body 3 is provided with the conductors 6 to form the rotor winding; thus the retaining ring insulation 50 and the liner sheet 8 are connected around the rotor body 3.

[0036] When the retaining ring 9 is connected above the retaining ring insulation 50, it is usually not needed an exact positioning of the borders 14 of the parts 10 because:

• the liner sheet damages neither the insulation of the portions 7 nor the retaining ring insulation 50, because compression (and thus risks of damages) only occurs over a very limited zone of the portions 7 (the part overlapping the borders 14) or over the zones of the retaining ring insulation 50 between the portions 7 and the borders 14;
• the risk that the pole separation wedges damage or break the retaining ring insulation is reduced, because the liner sheet prevents rotation of the pole separation wedges and therefore it prevents high stress.

[0037] Naturally the features described may be independently provided from one another.

[0038] In practice the materials used and the dimensions can be chosen at will according to requirements and to the state of the art.

REFERENCE NUMBERS

[0039] 

1

rotor

2

longitudinal axis

3

rotor body

4

rotor active part

5

rotor shafts

6

conductors

7

portions

8

liner sheet

9

retaining ring

10

parts

12

front border

13

rear border

14

lateral borders

22

seat

23

mounting stop

25

pole separation wedges

26

gap

27

radial axis

28

center of gravity

30

spring

50

retaining ring insulation

51

damper ring

52

damper finger sectors

F

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Claims

1. A rotor (1) for an electric machine comprising a rotor body (3) with a longitudinal axis (2), conductors (6) on the rotor (1)
a liner sheet (8) around the rotor body (3) and conductors (6),
characterised in that
the liner sheet (8) has parts (10) with lateral borders (14) that are not parallel to the longitudinal axis (2).

2. The rotor (1) of claim 1, characterised in that each part (10) of the liner sheet (8) has a front and rear border (12, 13) respectively facing the rotor body (3) and facing away from the rotor body (3), and lateral borders (14).

3. The rotor (1) of claim 2, characterised in that the lateral borders (14) of different parts (10) of the liner sheet (8) face each other.

4. The rotor (1) of claim 1, characterised in that the lateral borders (14) are at an angle to the longitudinal axis (2).

5. The rotor (1) of claim 1, characterised in that the lateral borders (14) are saw shaped.

6. The rotor (1) of claim 1, characterised in that the lateral borders (14) are wave shaped.

7. The rotor (1) of claim 1, characterised in that each part (10) has a seat (22) for a mounting stop (23).

8. The rotor (1) of claim 7, characterised in that the mounting stop (23) is removably connectable during mounting to a part (10) of the liner sheet (8).

9. The rotor (1) of claim 7, characterised in that the mounting stop (23) is removably connectable to the rotor body (3).

10. The rotor (1) of claim 1, characterised in that pole separation wedges (25) are provided between adjacent portion (7) projecting from slots of the rotor body (3),
at least during operation a gap (26) is defined between adjacent lateral borders (14) of adjacent liner sheet parts (10),
the gap (26) is asymmetric to a radial axis passing through the center of gravity (28) of the pole separation wedge (25).

11. The rotor (1) of claim 10, characterised in that springs (30) are provided to circumferentially press the pole separation wedge (25),
the gap (26) is at the spring (30).

12. The rotor (1) of claim 1, characterised in that the lateral borders (14) are located at the pole separation centers.

Drawing